1. Field of the Invention
The invention relates to a device for holding the ends of the turns of a stator winding in a dynamoelectric machine, comprising a rotor and a stator, which stator has a laminated core with end-side stator core end plates, there being arranged in the laminated core in slots a stator winding which has bottom and top bars and whose ends overlap the laminated core axially, which holder has an inner ring which fits closely, directly or with the inclusion of a separator, against the ends of the turns of the stator winding, which ends expand like an internal taper, and which has a multipartite external support which is supported on the end face of the laminated core.
In this regard, the invention refers to a prior art such as follows, for example, from EP-A-0,432,720, or U.S. Pat. No. 5,140,740, which has the same tenor.
2. Discussion of Background
Fastening the ends of the turns of the stator windings (winding overhang) of turbo-generators is attended by certain problems because of the high loads to which these winding overhangs are exposed. The origin of these loads lies in electromagnetic force effects, in particular in the case of short circuiting, in vibration phenomena and in different thermal expansions of the stator bars with respect to the stator iron during operation. These loads lead sooner or later to instances of loosening and wear phenomena, which lead in the end to earth shorts and short circuits.
In order to improve the strength of the winding overhangs of large electric machines, a series of systems have been introduced, the majority of which operate using single-part rings made from insulating material as the central support element.
In the device for holding the ends of the turns of a stator winding in an electric machine according to DE-OS 1,613,125, an outer ring fits closely from outside against a portion of the external layers of the ends of the turns. An inner ring which is independent of the outer ring engages on the inner layers of the ends of the turns. In order to prevent mutual axial displacement of the two rings, provision is made of devices which are constructed as C-shaped bows and embrace the ends of the turns so that the two bows are joined. The two rings are screwed by means of axially extending holders which, for their part, are fastened to the end face of the stator laminated core.
The winding overhang holder according to U.S. Pat. No. 4,800,314 uses only one outer ring. The winding overhang ends are wedged and bonded with respect to one another in groups and are fastened to this outer ring by means of bands.
A further solution, provided in particular for retrofitting, of the support problem is the subject-matter of U.S. Pat. No. 5,140,740 or EP-A-0,432,720, which has the same tenor. The holder proposed there has an inner ring which fits closely against the ends of the turns of the stator winding, which ends expand like an internal taper. The external support consists of an at least bipartite ring, or of supporting beams which extend in the circumferential direction and are interconnected. Tie bolts, which engage on the inner ring and outer ring or the supporting beams, serve to brace the inner ring and external support. Alternatively, the outer ring and the tie bolt can be omitted (FIG. 4) in what is known. Together with the end bows of the winding overhang, the inner ring is then supported, with the interposition of chucking wedges, on angles which are fastened on the end face of the stator laminated core.
It is disadvantageous in both alternatives that they can be reclamped in the case of instances of loosening of the winding overhang unit only by means of a high outlay.